The electromagnetic spectrum associated with radio frequency communications ranges includes very low frequencies (VLF) of a few kilohertz through very high frequencies (VHF) beginning at a few tens of megahertz through the ultrahigh frequencies (UHF) up to several hundred megahertz. Television and CATV signals are typically in the VHF and UHF ranges.
Tuners designed for broadband television and CATV signals must be able to tune across a range of frequencies including the VHF and UHF ranges. One type of tuner used for television and CATV signals is a band switching tuner. The band switching tuner uses a number of band tuners each designed for tuning across a specific band of frequencies. The band switching tuner uses one band tuner for detecting signals within one band of frequencies and then switches to another band tuner in order to detect signals within another band of frequencies.
One disadvantage of the band switching tuner is that each band tuner must be calibrated for its associated band of frequencies.
Another disadvantage of the band switching tuner is that air core inductors are often used in the band tuners. Air core inductors are calibrated by bending, compression, or stretching once mounted to a circuit board. Thus one disadvantage of air core inductors is that hand tuning is often required for these band tuners.
Another disadvantage of air core inductors is sensitivity to vibration. The characteristic impedance, center frequency, and bandwidth of tuners based on air core inductors can vary when the tuner is subjected to small vibrations. Although the variance might not cause noticeable affects on the quality of an analog signal, such variance can cause significant distortion to the spectral content of a digital or digitally modulated signal.